Rotary mixing apparatus



Feb. 7, 1939. v R; J. c. BOUDRANT ROTARY MIXING APPARATUS Filed Sept.25, 1956 5 Sheets-Sheet 1 Feb. 7, 1939. R. J. c. BOUDRANT I ROTARYMIXING APPARATUS 3 Sheets-Sheet 2 Filed Sept. 23, 1936 i. i. -l i- 3 4Feb.7,1939. R. J. C.-BOUDRA'NT' ,14

ROTARY MIXING APPARATUS Filed Sept. 25, 1936 s sheets-sheet 3 PatentedFeb. 7, 1939 UNITED STATES PATENT OFFICE assignor to Socit d Electricitede Paris, Paris,

France, a. French joint-stock company Application 6 Claims.

This invention relates to rotary means for mixing pulverized coal withair in connection with burners fed with pulverized coal.

It is well known that the rapidity of combus- 5 tion of pulverized coaldepends upon the intimate mixing betweenthe air and the coal. This hasled to the construction of burners of the so-called turbulence type.

However, in the majority of these burners, the

O combustion is far from being perfect, thatbeing due to the lack ofhomogeneity of the stream or mixture comprising coal dust and primaryair.

During the passage of this mixture between the pulverizing mill orstorage hopper and the burner, the coal separates out partially in thestream and it is then very difiicult to mix the secondary air forcombustion in a proper manner with the stream of fluid highly chargedwith combustible and possessing a considerable momentum.

The object of the present invention is to provide an apparatus whichproduces a mixture as homogeneous as possible between the air and thefuel immediately in front of the delivery to the burner.

The apparatus is composed essentially of two helically-bladed rotorshaving two, three or more blades (according to the diameter of the pipesystem) inclined upon their axes at angles from 30 to 60 according tothe speed of the fluid. The two rotors are of opposite hand to oneanother and consequently rotate in opposite directions by the eflEect ofthe fluid current impinging on the blades.

There results therefrom an energetic mixing up of the fluid inconsequence of the eddies thus created.

The apparatus is indeed based upon the difference of velocity existingbetween the carrier air and the coal carried therein, which produces atthe outlet from the first rotor a substantially homogeneousconcentration in eachconcentric layer round the axis of the apparatus.The eddies created at the entry to the second rotor ensure a completestirring up of the mixture.

With a pulverized-coal burner of the so-called turbulent type, in whichthe discharge of primary air into the combustion chamber takes placethrough a vertically elongated opening of considerable height and smallwidth, the unburnt solid particles amount to about 3 percent of theSeptember 23, 1936,'Serial No. 102,215 In France October 3, 1935 ing ofthe flame, an increase of 100 C. in the mean temperature of this latter,and a considerable reduction of the unburnt particles which have beenbrought down to about 1 percent of the coal consumption.

Upon the accompanying drawings, to which reference is made in thesubsequent description, Figs. 1 to 3 represent a first example ofcarrying out my invention:

Fig. 1 is a plan view of the mixer;

Fig. 2 is a corresponding vertical section along the axis 22 of Fig. 1;

Fig. 3 shows the mixer device placed upon a burner;

Figs. 4 to 6 represent another example of carrying out the invention,which obviates the rapid abrasion of the mechanical parts by thepulverized coal;

Fig. 4 is a vertical section taken along the axis 44 of Fig. 5;

Fig. 5 is a'plan View of the mixer; and

Fig. 6 is a partial view on a larger scale, of a section through themixer shown in Fig. 5.

Referring to Figs. 1, 2 and 3, a flat ring D inserted at the entry H tothe burner E, is cut out to the internal diameter of the pipe Isupplying the pulverized coal and primary air; upon this ring, there isfixed a chassis A, composed of two headers a c and three cross bars b b1)",- adapted to extend into the burner entry H. Two single cone-centersc c" and a double cone center mounted in the cross bars, receive thehardened steel pivots of the axes d, d of the two helically bladedrotors F and G. The single cone centers are constituted by theextremities of adjustable screws, secured by lock nuts 0.

The helically bladed rotors F and G, of opposite hand, are shownprovided with three blades each, these blades being inclined at 45 tothe axis.

. The arrow J in Figs. 2 and 3 indicates the direction of supply of thepulverized coal and primary air.

In the modification shown in Figs. 4, and 6, the tworotors 30, 3],fitted with helical blades I, 2, of opposite hand, and composing therotary mixer, are movable around a common shaft 3, Fig. 4.

The rotors 30, 3| are each screwed upon a hub 20, connected to the shaft3 by suitable bearings,'for example ball bearings 4, 5 (Figs. 4 and 6).These bearings are each fixed to one extremity of the shaft 3 by meansof nuts 3, with lock nuts or other devices to prevent unlocking, andprotected by a hub cap 2|. t

On the one hand, a felt washer 6 placedin a taken groove formed insidethe hub 20, Fig. 6, prevents the loss of lubricant along the shaft 3.

On the other hand, the shaft 3 possesses a central channel 1, closed atits two extremities 8, 9, by any suitable device. communication with acompressed air line by a tube II Figs. 4, 5 and 6.

The compressed air thus injected into the channel l escapes through twoseries of orifices I I, I2,

Figs. 4 and 6, each corresponding to one rotor.

These orifices to the number of six to ten for each rotor, and arrangedin a ring, blow air under pressure into an annular chamber l3 formed inthe hub 28 and thus maintain in that chamber a pressure greater thanthat existing in the pipe conveying the pulverized coal, thus avoidingany access of dust to the felts and bearing chambers.

In order to obtain absolute protection against the entrance of dust,with a minimum of expenditure of compressed air, the annular clearancebetween the outlet at the rim of the chamber l3 and the shaft 3 must beas small as possible.

Having regard to this small clearance, it is indispensable that thisannular rim shall be cut to a knife edge, as indicated in Figs. 4 and 6,or shall assume any other suitable form, in order to reduce the frictionto a minimum in case particles of coal should happen to collect upon thefixed or movable external parts of the apparatus as a result of greasydeposits from the oil which may be carried with the compressed air.

Figs. 4 and 5 show the simple method of mounting the rotary mixer whichhas just been described, in a pipe conveying air and pulverized coal.

A ring M is fixed in the pipe H; a channel member I 5- is formed on onediameter of this ring and is integral with the latter at its twoextremities.

The channel member I 5 is pierced at its center with a hole into whichthe shaft'B can be passed. Ihis shaft 3 is fixed at its center upon thechannel member l5 by means of the shoulder 22 integral with the shaft 3,and a nut 56 locked by the screw 23, Fig. 6. The rotors 1, 2, and thetube H), can then be mounted in place.

A semi-cylindrical piece N, Fig. 5, of a height slightly greater thanthat of the mixer, can be cut out of the pipe ll supplying thepulverized coal and air, this loose piece being then refitted by the aidof a cover plate l8, in order to allow erecting and taking down theapparatus during inspection, without having to dismantle a pipe systemof large diameter.

It is naturally permissible, without departing from the scope of theinvention, to provide modifications operating practically in the samemanner as the examples described above. 7

The number of blades 1, 2, on the respective rotors 38, 3|, and theirinclination can vary; they are in fact to be determined according toeach particular case.

There can also be provided a larger number of rotors in series, but theincrease of turbulence is slight whereas the loss of head risesconsiderably.

The apparatus is naturally applicable to any type of burner, whether ofturbulent or of ordinary type, and can be placed either upon the pipesupplying fuel and primary air, or at a position after the admission ofall or part of the secondary am What I claim is:

1. In combination with a pulverized coal burns er, a mixer mounted in apipeconveying the fuel and primaryair to the burner, saidmixer com-This. channel is in prising a frame, a pair of helically bladed rotorsarranged in series and closely spaced along said pipe, bearings for saidrotors carried by said frame, said rotors being rotatable by the currentof air and arranged to rotate in opposite direc tions on said bearings,and means for continuously supplying air under pressure to the interiorof said bearings to prevent coal dust from entering said bearings.

2. An apparatus for burning pulverized coal comprising a burner, a mixerthrough which the powdered coal and primary air travel to said burner,said mixer comprising a frame, a shaft carried by said frame andarranged coaxially of the current of coal-laden primary air, a pair ofhelically bladed rotors arranged in series, bearings for said rotorscarried upon said shaft, said rotors being rotatable by the current ofcoal-laden air, means for delivering compressed air to the interior ofsaid bearings, and means for discharging said compressed air from saidbearings to exclude said coal-laden air from said bearings.

' 3. In combination with a pulverized coal burner, a rotary mixer havinga. conduit through Which the coal and primary air travel to the burner,a framemounted in said conduit, a hollow shaft secured to said frame,said shaft being coaxial in relation to said conduit and having its endsprojecting in opposite directions from said frame, a pair of rotorsmounted in series upon said projecting ends, said rotors comprisinghelically bladed hubs and being rotated in opposite directions by thecurrent of air in said conduit, means for delivering compressed air tothe interior of said shaft adjacent to said frame, said compressed airhaving access through the projecting ends of said hollow shaft to theinterior of said hubs, and means for passing said compressed air betweensaid hubs and said shafts.

4. For use with a pulverized coal burner, a rotary mixer having aconduit through which the coal and primary air travel to the burner, aframe adapted to be mounted in said conduit, a hollow stationary shaftsecured to said frame, said shaft being coaxial in relation to saidconduit and having its ends projecting in opposite directions from saidframe, a pair of rotors mounted upon said projecting ends, helicalblades projecting from the hubs of said rotors, said rotors beingarranged in series, revoluble in opposite directions around saidprojecting ends, and driven by the current of air in said conduitimpinging on said blades, a hub cap secured to each of said rotors overthe respective end of said shaft, an annular chamber in each of saidrotors at the end remote from said hub cap, said annular chambersclosely surrounding said hollow stationary shaft, said hollow shaftbeing provided with passages extending from the bore outwards tocommunicate with said annular chambers, and means for supp-lying airunder pressure to the bore of said hollow shaft in communication withpassages and annular chambers.

5. A rotary mixing device for a powdered coal burner, comprising aconduit, a hollow shaft mounted coaxially' in said conduit, bearingsupon said hollow shaft, a pair of rotors of opposite hand arranged inseries in said conduit, each of said rotors including a hub and helicalblades projecting therefrom, said rotors being mounted at their hubs onsaid bearings and adapted to be rotatedin opposite directions by thecurrent of coal-charged'primary air passing along said conduit andimpinging on said blades, annular chambers-within'said hubs, saidchambers having walls tapering down almost to said shaft, said hollowshaft being provided with channels extending from the bore outwards intosaid annular chambers, packing washers arranged between said shaft andsaid hub to the side of said channels remote from said tapered walls,and means for supplying air under pressure to the bore of said hollowshaft in communication with said channels, annular chambers, and thespace between said shaft and the tapering Walls of said annularchambers.

6. A rotary mixing device for a powdered coal burner, comprising atubular conduit through which the powdered coal and primary air travelto said burner, a hollow stationary shaft secured in said tubularconduit, bearings upon said shaft, a pair of helically bladed rotors: ofopposite hand, arranged in series in said tubular conduit and eachhaving a hub with helical blades projecting therefrom, said rotors beingmounted at their hubs on said bearings and being rotated in oppositedirections by the coal-charged primary air travelling along saidconduit, annular chambers in said hubs, said chambers having wallstapering inwards close to said shaft, said hollow shaft being drilledwith small holes to provide a row of communicating channels between thebore and each of said annular chambers, hub caps secured to said hubs,said caps covering the outer ends of said hollow shaft, packing meansarranged between said shaft and said hub on the side of said channelsremote from the tapering walls of said annular chambers, and means forsupplying air under pressure to the bore of said hollow shaft incommunication with said channels, annular chambers and the space betweensaid shaft and the tapering wall of each said chamber.

ROBERT JEAN CHARLES BOUDRAANT.

